Over the years, there has been developed a substantial body of patent and other literature directed to the formation and properties of poly(aryl ethers) (hereinafter called "PAE"). Some of the earliest work such as by Bonner, U.S. Pat. No. 3,065,205, involves the electrophilic aromatic substitution (viz. Friedel-Crafts catalyzed) reaction of aromatic diacylhalides with unsubstituted aromatic compounds such as diphenyl ether. The evolution of this class to a much broader range of PAE's was achieved by Johnson et al., Journal of Polymer Science, A-1, vol. 5, 1967, pp. 2415-2427, Johnson et al., U.S. Pat. Nos. 4,108,837 and 4,175,175. Johnson et al. show that a very broad range of PAE's can be formed by the nucleophilic aromatic substitution (condensation) reaction of an activated aromatic dihalide and an aromatic diol. By this method, Johnson et al. created a host of new PAE's including a broad class of poly(aryl ether ketones), hereinafter called "PAEK's".
In recent years, there has developed a growing interest in PAEKs as evidenced by Dahl, U.S. Pat. No. 3,953,400; Dahl et al., U.S. Pat. No. 3,956,240; Dahl, U.S. Pat. No. 4,247,682; Rose et al., U.S. Pat. No. 4,320,224; Maresca, U.S. Pat. No. 4,339,568; Attwood et al., Polymer, 1981, vol 22, August, pp. 1096-1103; Blundell et al., Polymer, 1983 vol. 24, August, pp. 953-958, Attwood et al., Polymer Preprints, 20, no. 1, April 1979, pp. 191-194; and Rueda et al., Polymer Communications, 1983, vol. 24, September, pp. 258-260. In 1978, Imperial Chemical Industries PLC (ICI) commercialized a PAEK under the trademark Victrex PEEK. As PAEK is the acronym of poly(aryl ether ketone), PEEK is the acronym of poly(ether ether ketone) in which the phenylene units in the structure are assumed.
Thus PAEKs are well known; they can be synthesized from a variety of starting materials; and they can be made with different melting temperatures and molecular weights. Most of the PAEKs are crystalline and at sufficiently high molecular weights they are tough, i.e., they exhibit high values (&gt;50 ft-lbs/in.sup.3) in the tensile impact test (ASTM D-1822). They have potential for a wide variety of uses, and their favorable properties class them with the best of the engineering polymers.
Some PAEK's may be produced by the Friedel-Crafts catalyzed reaction of aromatic diacylhalides with unsubstituted aromatic compounds such as diphenyl ether as described in, for example, U.S. Pat. No. 3,065,205. These processes are generally inexpensive processes; however, the polymers produced by these processes tend to be brittle and thermally unstable. In contrast PAEK's made by nucleophilic aromatic substitution reactions are tough crystalline polymers. Nucleophilic aromatic substitution reactions for producing PAEK's are described in the following references:
Canadian Pat. No. 847963 describes a process for preparing polyarylene polyethers. The process comprises contacting equimolar amounts of a dihydric phenol and a dihalobenzenoid compound and at least one mole of an alkali metal carbonate per mole of dihydric phenol. The dihydric phenol is in situ reacted with the alkali metal carbonate to form the alkali metal salt thereof and the formed salt reacts with the dihalobenzenoid compound to form the polyarylene polyether in the usual fashion.
U.S. Pat. No. 4,176,222 describes the preparation of aromatic polyethers containing SO.sub.2 and/or CO linkages by a nucleophilic reaction utilizing a mixture of sodium carbonate or bicarbonate and a second alkali metal carbonate or bicarbonate. The alkali metal of the second alkali metal carbonate or bicarbonate has a higher atomic number than that of sodium. The second alkali metal carbonate or bicarbonate is used in amounts such that there are 0.001 to 0.2 gram atoms of the alkali of higher atomic number per gram atom of sodium. The process is stated to take place faster when the combination of sodium carbonate or bicarbonate and the second alkali metal carbonate or bicarbonate are used. Also the products are stated to be of high molecular weight using such a combination.
The patent describes in Example 17 that when the reaction is carried out using only sodium carbonate, a polymer is obtained having a reduced viscosity of 0.60 dl/g as measured in concentrated sulfuric acid at 25.degree. C. at a concentration of 1 gm/100 ml. However, it is stated in the patent that when the polymer was compression molded into a film, the film was brittle and dark grey in color. In Example 18 of the patent, the polymerization was carried out using potassium carbonate instead of sodium carbonate and a high molecular weight polymer was produced (reduced viscosity of 1.55 as measured in concentrated sulfuric acid at 25.degree. C. at a concentration of 1 gm/100 ml). However, the polymer was stated to contain a quantity of gel and also, the reaction vessel had acquired a black coating. In Example 19 of the patent, a mixture of potassium carbonate and sodium carbonate was used. The patent stated that the polymer produced had a high reduced viscosity and a tough off-white film was formed from it. Also, no gel was present in the polymer and the reaction vessel had not become discolored.
U.S. Pat. No. 4,320,224 also describes the production of aromatic polyetherketones in the presence of an alkali metal carbonate or bicarbonate in an amount providing at least 2 gram atoms of alkali metal per mole of starting bisphenol. The patent states that the sole use of sodium carbonate and/or bicarbonate is excluded.
U.S. Pat. No. 3,941,748 describes the use of alkali metal fluoride for preparing polyarylethers. The process requires that sufficient fluoride be present so that the total fluoride available (including that from any fluoroaryl monomers) be at least twice the number of phenol (--OH) groups. The examples show it to be, in general, a slow process. It is not one which is suitable per se for making PAEKs, see Control E, infra.
Imai, et al in Makromol Chem., 179,2989-2991, 1978 describe the preparation of polysulfones in dipolar aprotic solvents using at least 500 mole % of potassium fluoride based on the bisphenol. The process uses relatively low temperatures (about 100.degree. C.) to avoid polymer degradation but requires very long reaction times (48-70 hours).
U.S. Pat. No. 4,169,178 refers to the British counterpart of U.S. Pat. No. 3,941,748, i.e., British Pat. No. 1,348,630. The patent states that the amount of alkali metal carbonate required may be reduced in the preparation of aromatic polyethers by employing fluorophenols or difluorobenzenoid compounds as part or all of the halogen containing reactants. The patent states that the process gives faster reactions and higher molecular weights and less colored polymers than a process using potassium fluoride in place of potassium carbonate.
Thus, although potassium fluoride alone can be used for preparing PAEs it is alleged not to be effective enough since it requires long reaction times, does not result in high molecular weight and provides more than the desired amount of color in the PAE. In addition, it is not effective in the nucleophillic substitution reaction for forming PAEKs. Potassium fluoride in large concentrations is highly corrosive making selection of materials of construction of reactors expensive.